To investigate the effects of internal shear fragmentation on dry granular flow, in this study a series of ring shear tests were performed on quartz sand samples under different normal stresses (100 kPa, 200 kPa, and 300 kPa), shear displacements (3 m, 5 m, 10m, 15 m, and 20 m), and shear rates (30 deg min−1, 60 deg min−1, and 90 deg min−1). Next, the grain-size distributions, fractal dimensions, and microcharacteristics of the quartz sand before and after the experiments were compared and analyzed. The study results show that grain breakage under shearing preferentially occurs at the edges of the particles and forms a bimodal distribution in frequency grain-size distribution curves, which is consistent with observations of rock avalanches. The fine particles prevent the coarse particles from breaking, in turn leading to the ultimate grain-size distribution and stable fractal dimension (2.61) of quartz sand at relatively small shear displacements compared with the travel distance of rock avalanches. The results of this study suggest that the fragmentation of rock avalanches during the shear spread stage may be far less significant than previously believed. Therefore, the fragmentation effect is not considered to be a major factor of the hypermobility in the late stage of rock avalanches.

Rock–ice avalanches have increased in recent years due to global warming. On 12 March 2004, a massive failure of rock mass (9.1×106 m3) originated on the south slope of Yulong Mountain in Yunnan Province and eventually formed the Ganheba rock–ice avalanche, with an H/L ratio of 0.4. In this study, the geomorphological characteristics, sedimentary characteristics, and emplacement process of the Ganheba rock–ice avalanche were analyzed based on remote sensing interpretation, field investigation, and 2D discrete element modeling. This study suggests that long-term effects, including historical seismic effects and freeze–thaw action, were the key factors in the occurrence of this landslide. Interesting landforms and sedimentary structures found in this case, such as lateral ridges, superelevation, and boat rocks, were used to explain the characteristics of the velocity and the thinning spreading process of the avalanche mass. The numerical simulation further revealed that the entire movement of this rock–ice avalanche lasted about 105 s, with a maximum front velocity of 82 m/s. The underlying substrate rather than the ice is considered to have contributed to the hypermobility of the Ganheba rock–ice avalanche. The developed fissures, complex topography, and basal friction were determined to control the progressive fragmentation in this case. Meanwhile, the kinematic process of the Ganheba rock–ice avalanche was divided into four stages: failure and acceleration, collision deceleration, deceleration spreading, and deformation. The findings of this study contribute to an understanding of the evolution of glacier-related hazards in the high-mountain region.